1. The Field of the Invention
This invention relates to a web process control and detection apparatus, and more particularly to that class utilizing moving sensors and detectors across the surfaces of the web as the web is being transported in a direction parallel to the longitudinal marginal edges of the web.
2. Description of the Prior Art
The prior art abounds with apparatus utilized to measure web characteristics as the web travels in the direction of web processing.
U.S. Pat. No. 3,190,261, issued on June 22, 1965 to G. F. Ziffer teaches a pair of web measuring devices comprising a detector and a source mounted on the three ends of a "U" shaped structure travelling horizontally across the surface, travelling transverse to direction of travel of a web and spanning the upper and lowermost surfaces thereof.
U.S. Pat. No. 3,332,279, issued on July 25, 1967 to D. J. Tompos et al, discloses a similar pair of electronic units which travel directly transverse to web direction utilizing a beam as a support therefore. A light sensing apparatus detects when the sensors reach the marginal edge of the web and cause the opening of the sensor above the uppermost surface of the web thereby preventing tearing of the web due to a closely located sensor face as the sensor face passes from beyond the marginal edge to a position directly over the web. Both aforementioned inventions, though completely scanning the web from edge to edge in a transverse direction, suffer a common deficiency in being unable to provide directly a linear output directly transverse to the web direction, and utilize a comples mechanical probe positioning device which, due to its reciprocating ability, creates undue vibration and complicated and expensive transporting mechanisms therefore.